Transistor Gate-Drain Overlap Reduction for LCD Drivers
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Solution Overview
Problem
In liquid crystal display (LCD) devices using an amorphous silicon thin film transistor (a-Si TFT) as a gate driver, the parasitic capacitance between the gate and drain electrodes is high, leading to malfunctions and difficulties in forming the gate driver circuit, especially in larger devices, where the size of the transistors required increases parasitic capacitance and affects the gate line's operation.
Innovation Solution
The design of a transistor with a control electrode and two current electrodes, where the second current electrode is electrically insulated and partly overlaps with the control electrode, and the first current electrode has a specific shape to reduce parasitic capacitance, allowing for a minimized channel width and length, thereby reducing the parasitic capacitance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the size of the transistor is increased to drive larger LCD devices, then the driving capability is improved, but the parasitic capacitance increases causing malfunction
Solution Approach 1:
The transistor structure is segmented into distinct functional regions: a body portion for main current flow and hand portions extending in the channel direction. This segmentation allows the channel width to be effectively increased through hand portions while maintaining controlled parasitic capacitance by limiting overlap in the body portion.
Solution Approach 2:
The transistor design adds a dimensional element by extending hand portions in the channel direction (length dimension) rather than simply increasing width. This allows driving capability to be enhanced through extended hand portions while the body portion's controlled overlap maintains acceptable parasitic capacitance levels.
2Object-affected harmful factors
If the channel width and length are minimized to reduce parasitic capacitance, then the parasitic capacitance is reduced, but the transistor size becomes too small for reliable operation
Solution Approach 1:
The transistor is divided into a body portion and hand portions, where the body portion maintains sufficient dimensions for reliability while the hand portions extend the effective channel width. This segmentation allows the active channel width to be increased without proportionally increasing the overlapping area that generates parasitic capacitance.
Solution Approach 2:
Different regions of the transistor have different overlap characteristics: the body portion has controlled overlap to limit parasitic capacitance, while the hand portions extend without proportional overlap increase. This local quality differentiation allows effective channel width enhancement while maintaining acceptable parasitic capacitance levels.
3Ease of manufacture
If conventional transistor structures are used in gate driver circuits, then the manufacturing process is straightforward, but parasitic capacitance causes circuit malfunction
Solution Approach 1:
The transistor structure with body and hand portions can be manufactured using standard photolithography and thin-film deposition processes. The segmented design is achieved through pattern definition in the electrode layers, maintaining compatibility with existing manufacturing processes while improving circuit reliability.
Data Source
AI summary
A transistor includes a control electrode, a first current electrode and a second current electrode. The control electrode includes a body portion, and first and second hand portions protruded from first and second ends of the body portion, respectively. The first current electrode is electrically insulated from the control electrode and disposed over a region between the first and second hand portions of the control electrode. A portion of the first current electrode is overlapped with a portion of the control electrode. The second current electrode is electrically insulated from the control electrode and partially overlapped with the body portion, the first hand portion and the second hand portion of the control electrode. Therefore, parasitic capacitance is reduced.