Thin-Film Transistor Source Contact Layout for Smaller Display Pixels
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Solution Overview
Problem
Current thin film transistors face challenges in minimizing footprint size while maintaining the ability to express good gray scale levels, particularly in high-resolution display devices, due to the limited space required for connecting the source electrode, active layer, and light blocking layer.
Innovation Solution
A thin film transistor substrate configuration is introduced, featuring a lower hole in the active layer that allows the source electrode to penetrate and connect with the light blocking layer, along with an upper hole in the insulating layer, enabling electrical connection between the active layer, source electrode, and light blocking layer, reducing the overall footprint and enhancing gray scale expression.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of moving object
If the source electrode is electrically connected to the light blocking layer through a conventional configuration, then the transistor can function, but the footprint size increases and gray scale expression is limited
Solution Approach 1:
The source electrode is configured with an upper portion and a lower portion positioned at different vertical levels (dimensions). The lower portion is embedded in the active layer at a first depth, while the upper portion is positioned at a second depth above the first. This vertical dimensionality allows the source electrode to connect the active layer to the light blocking layer without requiring additional horizontal space, thereby reducing footprint size while maintaining proper electrical connection for gray scale expression.
Solution Approach 2:
The source electrode is nested within the active layer structure. The lower portion of the source electrode is embedded inside the active layer, and the upper portion extends above it. This nesting configuration allows the connection structure to be integrated within the existing transistor architecture rather than adding external connection elements, reducing overall footprint while maintaining functionality.
2Area of moving object
If the transistor size is reduced for high-resolution display, then pixel density increases, but the space required for source electrode connection becomes insufficient
Solution Approach 1:
By utilizing the vertical dimension with the lower portion at a first depth and the upper portion at a second depth within the active layer, the connection structure achieves the necessary electrical connectivity without requiring additional horizontal space. This allows miniaturized transistors to maintain proper source electrode connections despite reduced footprint dimensions.
Solution Approach 2:
The source electrode is segmented into distinct upper and lower portions with different depth positions within the active layer. This segmentation allows each portion to perform its specific function - the lower portion provides embedded connection while the upper portion provides external connectivity - without requiring a single large horizontal structure, thus enabling smaller transistor implementation.
3Reliability
If the source electrode contact area with the active layer is increased, then on-current and brightness improve, but the transistor footprint increases
Solution Approach 1:
The increased contact area is achieved through vertical extension rather than horizontal expansion. The lower portion of the source electrode is positioned at a first depth within the active layer while the upper portion is at a second depth, creating an extended contact interface along the vertical dimension. This allows improved on-current and brightness through larger contact area without increasing the horizontal footprint of the transistor.
Data Source
AI summary
A thin film transistor substrate for a display device can include a light blocking layer disposed on a substrate, an active layer overlapping with the light blocking layer, a first lower hole penetrating through the active layer, a gate electrode overlapping with the active layer, a source electrode penetrating through the active layer and contacting with the light blocking layer, an insulating layer disposed on the active layer, and a first upper hole penetrating through the insulating layer. Also, the source electrode includes a first lower electrode disposed in the first lower hole and a first upper electrode disposed in the first upper hole, in which a width of the first upper electrode is greater than a width of the first lower electrode.