Dual Oxide Semiconductor TFT Substrate for Bezel and Power Optimization
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Solution Overview
Problem
Oxide semiconductor thin-film transistors (TFTs) used in display devices face challenges with low mobility and reliability, particularly under negative bias illumination stress, and require materials with different characteristics for various demands such as low power consumption and small circuit size.
Innovation Solution
A thin-film transistor substrate is designed with two types of oxide semiconductor TFTs on the same substrate, one with high mobility for peripheral circuits and another with a wide bandgap for display regions, using different oxide semiconductor materials for each, and specific layer configurations to enhance reliability and reduce leakage current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If oxide semiconductor TFTs are used to achieve low power consumption, then leakage current is reduced and power consumption decreases, but mobility remains low compared to low-temperature polysilicon TFTs
Solution Approach 1:
The patent applies local quality by using different oxide semiconductor materials for different functional regions: IGZO material with wide bandgap is used in display regions where low leakage is critical, while ITZO material with higher mobility is used in peripheral circuits where driving capability is important. This allows each region to have optimized material properties matching its functional requirements.
Solution Approach 2:
The invention segments the TFT substrate into multiple regions with different oxide semiconductor materials. The display region uses IGZO-based TFTs for low power consumption, while peripheral circuit regions use ITZO-based TFTs for high mobility. This segmentation resolves the contradiction by allowing different material optimizations in different functional areas.
2Ease of manufacture
If a single oxide semiconductor material is used throughout the substrate, then manufacturing is simplified, but it is impossible to simultaneously optimize for both low power consumption and high mobility in different regions
Solution Approach 1:
Different oxide semiconductor materials are selectively applied to different regions: IGZO for display regions requiring low leakage, and ITZO for peripheral circuits requiring high mobility. This local differentiation enables functional optimization while maintaining a relatively streamlined manufacturing process.
Solution Approach 2:
The patent employs composite material strategy by combining multiple oxide semiconductor materials (IGZO and ITZO) on the same substrate. Each material contributes its advantageous properties to specific regions, creating a composite structure that achieves both low power consumption and high mobility in different functional areas.
3Reliability
If oxide semiconductor TFTs with wide bandgap are used for display regions, then reliability under negative bias illumination stress is improved, but circuit size may increase due to material limitations
Solution Approach 1:
The patent applies IGZO material with wide bandgap specifically in display regions where reliability under negative bias illumination stress is critical, while using ITZO material with higher mobility in peripheral circuits. This local optimization achieves high reliability where needed without unnecessarily increasing overall circuit size.
Solution Approach 2:
The invention changes material parameters (bandgap width, mobility) based on functional requirements. Display region TFTs use materials with wider bandgap for reliability, while peripheral circuit TFTs use materials with higher mobility for compact sizing. This parameter optimization resolves the contradiction between reliability and circuit size.
Data Source
AI summary
A thin-film transistor substrate includes an insulating substrate, a first insulating layer, a first thin-film transistor including a first oxide semiconductor film, a second insulating layer located upper than the first insulating layer, and a second thin-film transistor including a second oxide semiconductor film different in composition from the first oxide semiconductor film. At least a part of the first oxide semiconductor film is provided above and in contact with the first insulating layer. The first insulating layer is the uppermost insulating layer among insulating layers located lower than and in contact with the first oxide semiconductor film. At least a part of the second oxide semiconductor film is provided above and in contact with the second insulating layer. The second insulating layer is the uppermost insulating layer among insulating layers located lower than and in contact with the second oxide semiconductor film.