Semiconductor Memory Device Dummy Cell Threshold Control
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Solution Overview
Problem
Current semiconductor memory devices face limitations in integrating multiple strings on a substrate, leading to challenges in increasing threshold voltages efficiently, which affects leakage current characteristics and program disturbance phenomena.
Innovation Solution
A semiconductor memory device with a string comprising a drain select transistor, multiple drain and source side dummy memory cells, and a source select transistor, where a circuit applies operation voltages to increase threshold voltages using a hot carrier injection mechanism, improving leakage current characteristics and program efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If multiple strings are vertically formed on a substrate to increase integration, then the degree of integration is improved, but the complexity of controlling threshold voltages and managing leakage current increases
Solution Approach 1:
The patent applies preliminary action by increasing the threshold voltage of dummy memory cells before the main memory cell programming operation. The dummy memory cells are programmed first to establish higher threshold voltages, which then prevent unwanted programming of unselected memory cells during the subsequent main programming operation, thereby reducing program disturbance effects.
Solution Approach 2:
The patent uses dummy memory cells as intermediary elements between the select transistors and the main memory cells. These dummy cells serve as a mediator to control and manage the electric fields and carrier distributions, preventing direct interference between adjacent memory cells during programming operations.
2Reliability
If threshold voltages of dummy memory cells are increased to reduce program disturbance, then leakage current characteristics are improved, but the programming operation time increases
Solution Approach 1:
The threshold voltage increase of dummy memory cells is performed as a preliminary action before the main programming operation. By pre-programming the dummy cells to have higher threshold voltages, the patent establishes the necessary protective conditions in advance, which then reduce program disturbance during the main operation without requiring extended programming time.
3Reliability
If hot carrier injection mechanism is used to increase threshold voltages, then program disturbance is reduced, but energy consumption increases
Solution Approach 1:
The patent applies local quality by selectively applying high energy voltage only to the dummy memory cells and not to all memory cells simultaneously. The high voltage is localized to the dummy cells during their programming phase, allowing threshold voltage increase through hot carrier injection only where needed, thereby reducing overall energy consumption compared to programming all cells at high voltage.
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
The solution enhances leakage current characteristics and improves program disturbance phenomena by increasing threshold voltages, thereby enhancing the overall performance of the semiconductor memory device.
Implementation Method 1
The string comprises control logic configured to control the circuit to increase a first threshold voltage of the first dummy memory cell and to increase a second threshold voltage of the second dummy memory cell. The first threshold voltage and a second threshold voltage increase by a hot carrier injection mechanism.
Data Source
AI summary
A semiconductor memory device and an operating method thereof are set forth. The semiconductor memory device includes a memory cell array with a string. The string comprises a first dummy memory cell and a second dummy memory cell. A circuit is configured to provide a program voltage and one or more operation voltages to the string during a program operation. Control logic is configured to control the circuit to increase a first threshold voltage of the first dummy memory cell and to increase a second threshold voltage of the second dummy memory cell. The first threshold voltage and a second threshold voltage increase by a hot carrier injection mechanism.