Oxide TFT Substrate Insulating Layer for Mobility and Threshold Uniformity
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Solution Overview
Problem
Thin film transistors using amorphous silicon have low charge mobility, making fast-operating driving circuits difficult, while those using poly-silicon have non-uniform threshold voltage, requiring additional compensation circuits.
Innovation Solution
A thin film transistor substrate with a first semiconductor layer of oxide semiconductor material, a gate insulating layer patterned to correspond to the channel area, and a second insulating layer with an inorganic control layer having a lower density than the first inorganic layer to absorb moisture and control hydrogen and oxygen diffusion, improving charge mobility and threshold voltage uniformity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If an active layer is formed of amorphous silicon, then the manufacturing process is simpler, but charge mobility is low making fast-operating driving circuits difficult to implement
Solution Approach 1:
The patent employs a composite insulating layer structure combining inorganic layers (such as silicon oxide, silicon nitride) and organic layers (such as polyimide, benzocyclobutene). This composite structure provides both the moisture barrier properties of inorganic materials and the stress control capabilities of organic materials, thereby protecting the oxide semiconductor and maintaining high charge mobility while enabling straightforward manufacturing processes.
Solution Approach 2:
The patent carefully controls the density parameters of the inorganic control layer, specifying that it should have a lower density than the first inorganic layer. This parameter control optimizes the layer's ability to absorb moisture while maintaining structural integrity. Additionally, the thickness of each layer is precisely controlled to achieve the desired protective function without compromising manufacturing simplicity.
2Speed
If an active layer is formed of poly-silicon, then charge mobility is increased, but threshold voltage becomes non-uniform requiring additional compensation circuits
Solution Approach 1:
The inorganic control layer acts as an intermediary between the oxide semiconductor and the external environment. By positioning this layer with lower density between the oxide semiconductor and moisture sources, it mediates the interaction by absorbing excess moisture, thereby preventing threshold voltage shifts and maintaining uniformity while allowing the oxide semiconductor to achieve high charge mobility.
Solution Approach 2:
The multi-layer insulating structure creates a protected, inert environment around the oxide semiconductor by blocking moisture and oxygen diffusion. This protective atmosphere prevents degradation of the semiconductor material, ensuring both high charge mobility and uniform threshold voltage characteristics without requiring compensation circuits.
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
Enhances the characteristics of thin film transistor circuits by increasing charge mobility and uniformity of threshold voltage, thereby improving the performance of display apparatuses.
Implementation Method 1
The inorganic control layer has a lower density than a density of die first inorganic layer
Data Source
AI summary
A thin film transistor substrate includes a first semiconductor layer disposed on a substrate and having a first channel area, a first source area and a first drain area. A first gate electrode is disposed above the first semiconductor layer and overlaps the first channel area. A first electrode layer is disposed above the first gate electrode and electrically connects to at least one of the first source area and the first drain area. A second insulating layer is disposed between the first gate electrode and the first electrode layer. The second insulating layer includes an inorganic control layer and a first inorganic layer arranged on the inorganic control layer. The inorganic control layer has a lower density than a density of the first inorganic layer.