Dummy Select Transistor TCO Bias for NAND Program Disturb
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Solution Overview
Problem
In non-volatile storage systems, particularly in NAND strings, program disturb issues arise due to temperature-dependent changes in threshold voltage of dummy select transistors, affecting their conductivity during program and read operations, leading to potential operational disruptions.
Innovation Solution
Applying a voltage with a positive temperature coefficient (Tco) to the control terminal of dummy select transistors during program operations helps maintain the threshold voltage, ensuring the dummy select transistors remain conductive and do not interfere with program or read operations by reducing or eliminating program disturb.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a fixed voltage is applied to the control terminal of dummy select transistors, then the circuit design is simple, but program disturb occurs due to temperature-dependent threshold voltage changes
Solution Approach 1:
The patent applies a voltage with a positive temperature coefficient to the control terminal of dummy select transistors. This voltage parameter changes with temperature to compensate for threshold voltage shifts, thereby preventing program disturb while maintaining circuit functionality.
Solution Approach 2:
Instead of using a fixed voltage, the patent employs a dynamic voltage that varies with temperature. The control voltage is adjusted in real-time based on temperature conditions, transforming the static voltage application into a dynamic compensation mechanism.
2Reliability
If no voltage is applied to dummy select transistors, then energy consumption is low, but threshold voltage drifts with temperature causing operational issues
Solution Approach 1:
The patent changes the voltage parameter from zero or fixed to a temperature-dependent positive Tco voltage. This parameter change stabilizes the threshold voltage across temperature variations while the energy consumption remains manageable due to the efficient voltage compensation mechanism.
3Reliability
If high voltage is applied to dummy select transistors to prevent program disturb, then reliability improves, but device stress increases
Solution Approach 1:
The patent uses a voltage with positive temperature coefficient that dynamically adjusts with temperature. This prevents the need for continuously high voltage application, as the voltage naturally compensates for threshold drift, thereby reducing overall device stress while maintaining reliability.
Solution Approach 2:
The dummy select transistors receive a voltage that automatically adjusts according to temperature conditions. The system self-regulates the voltage level based on thermal conditions, eliminating the need for external high-voltage forcing and reducing unnecessary device stress.
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 effectively mitigates program disturb in dummy select transistors, maintaining their conductivity and ensuring reliable operation across varying temperatures, thereby enhancing the stability and efficiency of memory operations.
Implementation Method 1
Applying a voltage having a positive temperature coefficient (Tco) to a control terminal of the dummy select transistor
Data Source
AI summary
Technology for applying a positive temperature coefficient (Tco) voltage to a control terminal of a dummy select transistor. The dummy select transistor resides on a NAND string having non-volatile memory cells and a regular select transistor. The dummy select transistor is typically ON (or conductive) during memory operations such as selected string program, read, and verify. In an aspect, the positive Tco voltage is applied to the control terminal of a dummy select transistor during a program operation. Applying the positive Tco voltage during program operations reduces or eliminates program disturb to the dummy select transistor. In some aspects, the dummy select transistor is used to generate a gate induced drain leakage (GIDL) current during an erase operation. In some aspects, the dummy select transistor is a depletion mode transistor.