Thin Film Transistor Substrate Light-Blocking Layer Design
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Solution Overview
Problem
In liquid crystal displays (LCDs), the active layers of thin film transistors are affected by light from backlight modules, leading to instability in electrical properties, particularly when top-gate transistors are exposed directly and bottom-gate transistors are damaged during electrode formation processes.
Innovation Solution
A thin film transistor substrate design featuring a light-blocking layer between the substrate and active layer, with the active layer recessed from the light-blocking layer's edge by 0.5 μm to 3 μm, and a gate insulating layer covering the active layer, along with source and drain electrodes electrically connected to the active layer, effectively blocking light and enhancing electrical stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If top-gate thin film transistors are used with active layers directly exposed to light, then the structure is simpler, but the active layer generates photo current affecting electrical properties
Solution Approach 1:
A light-blocking layer is introduced as an intermediary between the substrate and the active layer. This layer blocks light from reaching the active layer, preventing photo current generation while maintaining the top-gate transistor structure. The light-blocking layer serves as a mediator that resolves the conflict between structural simplicity and electrical stability.
2Reliability
If bottom-gate thin film transistors are used to block light, then electrical properties are improved, but the active layers are easily damaged in subsequent processes
Solution Approach 1:
Instead of placing the light-blocking function at the bottom gate as in conventional bottom-gate transistors, the light-blocking layer is inverted to be positioned at the substrate level before the active layer is formed. This inversion allows light blocking to be achieved without exposing the active layer to damage during subsequent electrode formation processes.
3Object-affected harmful factors
If the active layer edge is recessed from the light-blocking layer edge by 0.5 μm to 3 μm, then light-blocking efficiency is enhanced, but the manufacturing precision requirement increases
Solution Approach 1:
The light-blocking layer is formed first as a preliminary structure before the active layer is deposited. This preliminary action establishes a defined boundary that guides subsequent active layer formation, ensuring the required 0.5 μm to 3 μm recess is achieved through controlled deposition and etching processes.
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 light-blocking layer significantly improves the stability of the active layer by effectively blocking light from below, reducing damage and maintaining electrical properties, while the recessed edge enhances light-blocking efficiency.
Implementation Method 1
a light-blocking layer disposed on the substrate; an active layer disposed on the light-blocking layer and overlapped with the light-blocking layer
Data Source
AI summary
An embodiment of the invention provides a thin film transistor substrate includes: a substrate; a plurality of transistors on the substrate, wherein each of the transistors includes: a light-blocking layer on the substrate; an active layer on the light-blocking layer; a gate insulating layer on the substrate and covering the active layer; a gate electrode on the gate insulating layer and over the active layer; a source electrode on the substrate and electrically connected to the active layer; and a drain electrode on the substrate and electrically connected to the active layer.