FinFET Nonvolatile Memory Cell Split-Gate Threshold Control
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Solution Overview
Problem
The challenge in semiconductor devices is controlling the threshold voltage of FinFETs in nonvolatile memory cells with a split-gate structure, which affects data retention and memory characteristics due to the difficulty in independently setting the threshold voltages of selection and memory transistors.
Innovation Solution
A semiconductor device with a FinFET-based nonvolatile memory cell that includes a threshold voltage determination circuit and driver circuits to manage bias voltages, ensuring the selection transistor is brought into a stable OFF state by using a virtual reference potential to control the word line and source line voltages, thereby reducing leakage currents and improving data retention.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a FinFET is used in a nonvolatile memory cell with a split-gate structure, then excellent switching characteristics and stable operation are obtained, but it becomes difficult to control the threshold voltage of the selection and memory transistors independently
Solution Approach 1:
The gate electrode is segmented into two separate gates: a selection gate electrode and a memory gate electrode. This segmentation allows independent control of the selection transistor and memory transistor threshold voltages, resolving the contradiction by enabling separate voltage control while maintaining the FinFET's stable switching characteristics.
Solution Approach 2:
Different regions of the memory cell are given different electrical properties by applying different voltages to the selection gate and memory gate. The selection gate region controls access while the memory gate region controls data retention, allowing local optimization of threshold voltages for different functional requirements.
2Reliability
If the selection transistor has a negative threshold voltage to ensure stable OFF state, then leakage currents are reduced, but data retention property becomes difficult to control
Solution Approach 1:
A virtual reference potential is introduced as an intermediary to control the threshold voltage of the selection transistor. By using this virtual reference potential instead of directly controlling the selection gate voltage, the system can achieve stable OFF state with negative threshold voltage while maintaining controllability of data retention properties.
Solution Approach 2:
The threshold voltage control is achieved by changing the potential reference level rather than directly adjusting voltage magnitudes. The virtual reference potential allows the selection transistor to operate with a negative threshold voltage relative to the substrate potential, ensuring stable OFF state while the memory transistor's threshold voltage can be independently optimized for data retention.
Data Source
AI summary
Provided is a semiconductor device including nonvolatile memory cells each including a FinFET having excellent memory characteristics. The semiconductor device includes a semiconductor substrate, memory cells each formed in the semiconductor substrate and having a split-gate structure including an opposed-gate selection gate electrode, a memory gate electrode, and a pair of terminals, and a word line driver circuit which supplies a selection voltage to a selection gate electrode of the selected one of the memory cells and supplies a non-selection voltage to the selection gate electrode of the non-selected one of the memory cells. The word line driver circuit supplies, as the non-selection voltage, a voltage which is negative or positive relative to a potential in the semiconductor substrate so as to bring a selection transistor corresponding to the selection gate electrode of the non-selected memory cell into an OFF state.