Trench-Based TFT Array Substrate for LCD Flatness
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Solution Overview
Problem
Conventional thin film transistors in liquid crystal displays (LCDs) result in non-flat substrates, affecting liquid crystal orientations and reducing transmittance due to multiple layers and inadequate step coverage, leading to defects and shorts at electrodes.
Innovation Solution
A trench-based structure is formed in the substrate with a gate, gate dielectric layer, semiconductor layer, and doped semiconductor layer, where source and drain electrodes are connected on opposite sides of the channel, and a dual damascene trench configuration is used to improve flatness and reduce layer thickness in the display area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional TFT structure with multiple layers is used, then the transistor functionality is achieved, but the substrate becomes non-flat and transmittance is reduced
Solution Approach 1:
The patent embeds the TFT structure within a trench formed in the substrate, transitioning from a planar configuration to a three-dimensional embedded structure. This dimensional change allows the TFT to be housed within the substrate thickness rather than adding height, maintaining substrate flatness while preserving transistor functionality
Solution Approach 2:
The TFT components (gate electrode, gate insulating layer, semiconductor layer, source/drain electrodes) are nested within the trench structure, which is itself formed within the substrate. This nested arrangement consolidates multiple functional layers into a compact volume, avoiding the need for additional external layers that would reduce transmittance
2Reliability
If multiple layers are formed on pixels to achieve TFT functionality, then transistor operation is enabled, but transmittance and brightness are reduced
Solution Approach 1:
The patent extracts the TFT structure from the pixel surface and relocates it within the substrate trench. By removing the TFT layers from the optical path above the pixel, light transmission is no longer blocked by multiple TFT layers, thereby maintaining high transmittance and brightness while TFT operation is preserved within the substrate
3Ease of manufacture
If the second metal layer is formed with inadequate step coverage, then the fabrication process is simplified, but defects and shorts occur at source and drain electrodes
Solution Approach 1:
The patent performs preliminary actions by forming the gate electrode and gate insulating layer within the trench before forming the semiconductor and source/drain layers. This sequential preparation ensures proper step coverage is achieved at each stage, preventing defects before they occur while maintaining a manageable fabrication process
4Shape
If a trench-based structure is used to improve flatness, then substrate flatness is enhanced, but fabrication process complexity increases
Solution Approach 1:
The patent merges the TFT fabrication steps with the trench formation process. The gate electrode and gate insulating layer are formed as part of the trench filling process, and the semiconductor and source/drain layers are formed simultaneously within the trench confines. This merging of operations achieves substrate flatness without proportionally increasing fabrication complexity
Data Source
AI summary
A liquid crystal display array substrate. A trench is in a substrate. A gate, a gate dielectric layer, a semiconductor layer and a doped semiconductor layer are disposed in the trench, wherein the semiconductor layer comprises a channel. A source electrode and a drain electrode are respectively electrically connected to portions of the semiconductor layer on opposite sides of the channel.