Nonvolatile Memory Programming via Hot Hole Injection
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Solution Overview
Problem
Nonvolatile memory devices face challenges in efficiently programming and verifying threshold voltage distributions of transistors, leading to reliability issues due to wide voltage distributions and the need for precise control of programming operations.
Innovation Solution
A method for operating nonvolatile memory devices involves programming ground selection transistors with boosted voltages and negative gate voltages to reduce threshold voltage distributions, using hot hole injection operations and controlled voltage applications to limit voltage ranges within specific thresholds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single programming operation is applied to transistors in a cell string, then the programming process is simple, but the threshold voltage distribution remains wide and reliability is poor
Solution Approach 1:
The programming operation is segmented into multiple distinct programming operations. Each operation targets different transistors within the cell string (e.g., string selection transistors vs. memory cells) and applies different voltage conditions. This segmentation allows independent optimization of threshold voltage distributions for different transistor types, narrowing the overall voltage distribution and improving reliability without requiring a single complex operation.
Solution Approach 2:
Different programming operations are applied to different local regions (transistors) within the cell string based on their specific requirements. String selection transistors receive one set of voltage conditions while memory cells receive another. This local differentiation ensures that each transistor type receives the precise programming conditions it needs, achieving narrow threshold voltage distributions for all transistors in the string.
2Reliability
If multiple programming operations are applied to different transistors in a cell string, then the threshold voltage distribution is narrowed and reliability is improved, but the programming time increases
Solution Approach 1:
Multiple programming operations that would traditionally be executed sequentially are merged into a single operation cycle. The controller executes different programming operations for different transistors in parallel within the same time cycle, using separate word line activation sequences. This merging reduces the total programming time from the sum of individual operations to a concurrent execution window, maintaining narrow threshold voltage distributions while minimizing time loss.
Solution Approach 2:
The controller performs preliminary selection and preparation of transistors before applying programming voltages. By pre-activating specific word lines and configuring voltage conditions in advance, the system prepares the transistor array for efficient parallel programming. This preliminary action enables multiple programming operations to proceed concurrently without interference, reducing overall programming time while maintaining precision.
3Productivity
If high voltage is applied to program transistors, then the programming speed increases, but the risk of exceeding threshold voltage limits and causing reliability issues increases
Solution Approach 1:
The voltage application is made dynamic rather than static. The controller dynamically adjusts voltage levels and timing sequences based on the specific transistor being programmed and the current state of the cell string. Different voltage magnitudes are applied to different transistors at different times, with the system continuously monitoring to ensure threshold voltage limits are not exceeded. This dynamic control maintains high programming speed while ensuring reliability through real-time voltage management.
Solution Approach 2:
The system incorporates feedback mechanisms to monitor threshold voltage conditions during programming. The controller uses verify operations and voltage distribution monitoring to detect when transistors approach their voltage limits. Based on this feedback, the controller adjusts subsequent programming operations to prevent exceeding maximum threshold voltages. This feedback loop enables high programming speeds to be maintained without compromising reliability by preventing voltage limit violations.
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 narrows the threshold voltage distribution of transistors, enhancing the reliability of nonvolatile memory devices by ensuring that threshold voltages are controlled within target ranges, thereby improving programming efficiency and device reliability.
Implementation Method 1
The second programming may be a hot hole injection operation.
Implementation Method 2
applying a negative voltage to a gate of the target transistor
Data Source
AI summary
A method of operating a nonvolatile memory device includes: first programming a target transistor of a cell string of the nonvolatile memory device, wherein the target transistor has a first threshold voltage distribution after the first programming, and wherein the cell string includes a plurality of transistors; and second programming the target transistor of the cell string, wherein the first transistor has a second threshold voltage distribution after the second programming, wherein a width of the second threshold voltage distribution is less than a width of the first threshold voltage distribution.