Nonvolatile Memory Selection Transistor Threshold Control
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Solution Overview
Problem
Existing nonvolatile memory devices face challenges in accurately controlling and verifying the threshold voltages of selection transistors, leading to program disturbance issues due to the difficulty in finely controlling impurity distribution through ion implantation.
Innovation Solution
The implementation of a nonvolatile memory device with a control logic that programs and verifies the threshold voltages of selection transistors, allowing for the adjustment of threshold voltages during program operations and using verification voltages to ensure accurate programming, thereby reducing program disturbance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If ion implantation is used to control impurity distribution in selection transistors, then manufacturing capability is improved, but manufacturing precision deteriorates due to difficulty in finely controlling impurity distribution
Solution Approach 1:
The patent changes the approach from physical ion implantation to electrical parameter control. By applying program voltages to word lines and bit lines, the threshold voltage of selection transistors is controlled through electrical fields rather than physical impurity distribution. This allows precise control of transistor characteristics through voltage parameters (Vpgm, Vpass, Vb) without the limitations of ion implantation precision.
2Reliability
If threshold voltage control of selection transistors is implemented, then program disturbance is reduced, but device complexity increases due to additional control logic and verification steps
Solution Approach 1:
The patent makes the existing word lines and bit lines serve dual functions: both for memory cell programming and for selection transistor threshold voltage control. The same WL and BL lines used for memory operations are also used to apply program voltages for selecting strings, eliminating the need for separate control lines and reducing overall device complexity despite adding control functionality.
Solution Approach 2:
The patent implements verification operations where read voltages are applied to selected strings to verify that the threshold voltage control was successful. This feedback mechanism ensures that only properly selected strings are programmed, preventing program disturbance to unselected strings while maintaining reliable control through the verification step.
3Measurement precision
If verification of selection transistor threshold voltage is performed, then programming accuracy is improved, but operation time increases due to additional verification steps
Solution Approach 1:
The patent merges the verification of selection transistor threshold voltage with the memory cell read operation. By applying read voltages to both the memory cells and the selection transistors simultaneously, the verification is performed in conjunction with the programming operation rather than as a separate step, thereby reducing total operation time while maintaining verification accuracy.
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 enables precise control of threshold voltages, reducing program disturbance and improving the reliability of memory cell programming and reading operations.
Implementation Method 1
The depletion type transistor or the enhancement type transistor may be formed by an ion implantation manner.
Data Source
AI summary
According to example embodiments, a nonvolatile memory device includes a plurality of strings having a plurality of serially-connected selection transistors and a plurality of memory cells connected in series to one end of the serially-connected selection transistors. A control logic is configured to perform a program operation for setting a threshold voltage of at least one of the serially-connected selection transistors.