Select Gate Threshold Voltage Shift via Electric Field
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Solution Overview
Problem
In non-volatile memory systems, the voltage on a control gate of a memory cell adjacent to a select transistor can creep up after a sensing operation, creating an electric field that may lead to a permanent change in the threshold voltage of the select transistor, affecting the performance of memory array operations.
Innovation Solution
Generating an electric field between the select transistor and the adjacent memory cell by increasing the voltage on the select transistor's control gate and floating both the select gate and memory cell control gates, which prevents or reduces the permanent change in the threshold voltage of the select transistor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the voltage on the control gate of the memory cell is increased during sensing operation, then the sensing operation can be performed, but the voltage may creep up after the operation creating an electric field that permanently changes the threshold voltage of the select transistor
Solution Approach 1:
The patent applies preliminary anti-action by generating a counter electric field before the voltage creep can permanently affect the select transistor threshold voltage. After the sensing operation completes and before the control gate voltage fully creeps up, the system intentionally creates an opposing electric field between the select transistor control gate and the adjacent memory cell control gate. This preliminary counter-action prevents the harmful threshold voltage shift from occurring in the first place, rather than attempting to correct it afterward.
Solution Approach 2:
The patent utilizes parameter changes by dynamically adjusting the voltage levels on the select transistor control gate and adjacent memory cell control gate. The system changes the voltage parameters from their normal operating levels to create the compensating electric field. Specifically, it increases the voltage on the select transistor control gate relative to the adjacent memory cell control gate, thereby changing the electric field parameters to counteract the harmful effects of voltage creep.
2Stability of the object's composition
If the voltage on the select transistor control gate is increased to prevent threshold voltage shift, then the threshold voltage stability is improved, but additional voltage control steps are required
Solution Approach 1:
The patent implements self-service by utilizing the existing control gate structures and voltage control mechanisms that are already part of the memory device architecture. Rather than introducing entirely new components or complex external control systems, the invention repurposes the existing control gates of the select transistor and adjacent memory cell to generate the compensating electric field. The same voltage control circuitry that normally operates the memory device is used to implement the threshold voltage protection, making the system protect itself using its own built-in resources.
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 prevents or slows down the movement of charges that could alter the threshold voltage of the select transistor, thereby maintaining the integrity of memory cell operations and reducing program disturb issues.
Implementation Method 1
generating an electric field between a select transistor and a memory cell adjacent to the select transistor
Data Source
Figure 1A~1B
Figure 1C~1D
Figure 2A~2B
AI summary
Non-volatile storage systems and method of operating non-volatile storage systems are disclosed. A crept up voltage on a dummy memory cell control gate adjacent to a select gate is prevented, reduced, and/or discharged. In some aspects, the crept up voltage is not allowed to happen on the dummy memory cell next to the select gate after a sensing operation. In some aspects, the voltage may creep up on the dummy memory cell control gate after a sensing operation, but it is discharged. Reducing and/or preventing the crept up voltage may reduce the electric field between the dummy memory cell and select gate transistor. This may prevent, or at least reduce, changes in threshold voltage of the select gate transistor. Additional problems may also be solved by a reduction of the crept up voltage on the dummy memory cell control gates.