Vertical TFT Threshold Control Gates for Low-Leakage Memory Cells
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Solution Overview
Problem
Conventional volatile memory cells experience unwanted current flow even in the 'off' state due to challenges in achieving a high threshold voltage (Vt) while maintaining low leakage current (Ioff) and high drive current (Ion), particularly when using materials that cannot be effectively doped to modify Vt.
Innovation Solution
Incorporating threshold voltage control gates in vertical thin film transistors (TFTs) that can be externally biased to tailor the Vt, allowing for control of electrical characteristics without modifying the channel material's work function or doping, thereby achieving a high Vt, low Ioff, and high Ion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If doping is used to increase Vt in polysilicon channel, then Vt increases, but doping cannot be used with other channel materials that cannot be effectively doped
Solution Approach 1:
The patent changes the parameter of threshold voltage control from material composition (doping) to electrical biasing. By introducing a threshold voltage control gate that applies external electrical fields, the method achieves Vt adjustment without altering the channel material's chemical composition, making it compatible with undopable materials like oxide semiconductors.
Solution Approach 2:
The threshold voltage control gate acts as an intermediary between the control circuitry and the channel region. It mediates the interaction by generating electrical fields that penetrate the gate dielectric to modulate the channel's threshold voltage, enabling indirect control without direct material modification.
2Reliability
If work function difference is modified to increase Vt, then Vt increases, but this requires changing gate or channel material properties
Solution Approach 1:
The patent transforms the static threshold voltage (determined by fixed material work functions) into a dynamic parameter that can be adjusted in real-time through electrical biasing. The threshold voltage control gate enables continuous modulation of Vt during device operation, providing adaptability that fixed material properties cannot achieve.
3Productivity
If conventional transistors are used in volatile memory cells, then current flow is achieved, but unwanted current flow occurs even in the off state due to low Vt
Solution Approach 1:
The threshold voltage control gate creates a feedback mechanism where the control voltage applied to the threshold voltage control gate can dynamically adjust the transistor's threshold voltage based on operational requirements. This enables real-time optimization of the balance between drive current and leakage current suppression.
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 enables improved refresh and disturb properties by maintaining an effective channel area for high drive current while ensuring low leakage current, without sacrificing the channel area, thus enhancing the performance of semiconductor devices.
Implementation Method 1
The threshold voltage control gates are laterally adjacent opposing second sides of the channel region and are configured to receive an external bias to control a threshold voltage of the vertical TFT
Data Source
AI summary
A transistor comprising threshold voltage control gates. The transistor also comprises active control gates adjacent opposing first sides of a channel region, the threshold voltage control gates adjacent opposing second sides of the channel region, and a dielectric region between the threshold voltage control gates and the channel region and between the active control gates and the channel region. A semiconductor device comprising memory cells comprising the transistor is also disclosed, as are systems comprising the memory cells, methods of forming the semiconductor device, and methods of operating a semiconductor device.