Polycrystalline Silicon TFT Active Layer Thickness Control
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Solution Overview
Problem
Existing LCD devices face issues with thin film transistor property degradation due to thickness differences in the active layer, leading to instability and low carrier mobility, which affects production efficiency and suitability for driving circuits.
Innovation Solution
A method is introduced that forms a buffer layer on a substrate with an inorganic insulating material, followed by sequential layers of a gate electrode, gate insulating layer, active layer, and auxiliary active layer, using polycrystalline silicon and amorphous silicon to improve transistor reliability and reduce production costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the active layer thickness is increased to prevent property degradation, then transistor reliability improves, but production time increases due to longer deposition time
Solution Approach 1:
The invention changes the material parameter from amorphous silicon to polycrystalline silicon, which fundamentally alters the deposition characteristics and allows for thinner, more uniform layers that achieve the desired reliability without increasing production time
Solution Approach 2:
The invention uses a composite structure with multiple silicon layers (intrinsic and extrinsic polycrystalline silicon layers) with different properties, where each layer contributes to overall transistor performance while maintaining optimal thickness for fast production
2Ease of manufacture
If amorphous silicon is used for the active layer, then manufacturing is easier, but carrier mobility remains low affecting driving circuit suitability
Solution Approach 1:
The invention changes the crystalline structure parameter of the silicon material from amorphous to polycrystalline, which significantly improves carrier mobility while maintaining compatibility with standard semiconductor manufacturing processes
Solution Approach 2:
The invention creates different regions with different silicon crystal structures (intrinsic and extrinsic polycrystalline silicon) in specific locations within the active layer, optimizing carrier mobility in the channel region while maintaining ease of manufacture through standardized processes
3Ease of manufacture
If thickness difference is created in the active layer during manufacturing, then manufacturing process is simpler, but transistor properties degrade
Solution Approach 1:
The invention ensures uniform thickness across the active layer by using polycrystalline silicon deposition techniques that provide better thickness control compared to amorphous silicon, eliminating the need for compensating thickness differences
Solution Approach 2:
The invention performs preliminary crystallization of the silicon layer before subsequent processing steps, establishing uniform thickness and desired electrical properties early in the manufacturing process, which prevents property degradation without complicating later steps
Data Source
AI summary
Disclosed is a method of fabricating a display device that includes forming a buffer layer; forming a gate electrode of extrinsic polycrystalline silicon, a gate insulating layer, an active layer of intrinsic polycrystalline silicon and an auxiliary active layer of intrinsic amorphous silicon on the buffer layer; forming an ohmic contact layer of extrinsic amorphous silicon and contacting the auxiliary active layer, source and drain electrodes and a data line; patterning a first passivation layer, an insulating interlayer and the gate insulating layer to form a gate contact hole exposing the gate electrode; forming a gate line on the first passivation layer, made of a metal material, and contacting the gate electrode through the gate contact hole; forming a second passivation layer on the gate line; patterning the first and second passivation layers to form a drain contact hole exposing the drain electrode; and forming a pixel electrode on the second passivation layer in the pixel region and contacting the drain electrode through the drain contact hole.