TFT Substrate with Mixed a-Si and Oxide Semiconductor Layers
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Solution Overview
Problem
Current LCD manufacturing processes face challenges in producing thin film transistor (TFT) substrates with high mobility for drive circuits, leading to increased costs and limitations in downsizing due to the low mobility of amorphous silicon (a-Si) TFTs and the high temperature requirements of polycrystalline silicon (poly-Si) technologies, while oxide semiconductor TFTs suffer from optical degradation.
Innovation Solution
A thin film transistor substrate design that integrates a pixel TFT with a channel layer made of amorphous silicon and a drive TFT with a channel layer made of oxide semiconductor on the same substrate, utilizing a specific configuration of gate electrodes, contact layers, and semiconductor layers to achieve high mobility and reduce manufacturing costs, with a BCE process that allows for selective etching and uniformity of the a-Si channel layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If polycrystalline silicon (poly-Si) is used to achieve high mobility for drive circuits, then mobility is improved, but manufacturing cost increases and temperature requirements become too high
Solution Approach 1:
The patent applies different semiconductor materials to different regions of the substrate: amorphous silicon for pixel TFTs in the display region and oxide semiconductor for drive TFTs in the peripheral region. This local differentiation allows each region to have optimized properties - pixel TFTs benefit from the simplicity and low-temperature processing of a-Si, while drive TFTs benefit from the high mobility of oxide semiconductor without requiring expensive poly-Si processing
Solution Approach 2:
The patent changes the material parameter from conventional amorphous silicon to oxide semiconductor for the drive TFT channel layer. This parameter change enables high mobility (comparable to or exceeding poly-Si) while maintaining compatibility with low-temperature manufacturing processes and avoiding the high costs associated with poly-Si fabrication
2Ease of manufacture
If amorphous silicon (a-Si) is used for manufacturing, then manufacturing cost is reduced and temperature requirements are lowered, but mobility is insufficient for drive circuits
Solution Approach 1:
The patent differentiates material selection by functional region: a-Si is used for pixel TFTs where low cost and simple processing are priorities, while oxide semiconductor is used for drive TFTs where high mobility is critical. This resolves the contradiction by allowing a-Si to fulfill its role in cost-effective manufacturing while oxide semiconductor provides the necessary performance for drive circuits
3Reliability
If oxide semiconductor TFTs are used to achieve high mobility, then mobility is improved, but optical degradation occurs
Solution Approach 1:
The patent confines oxide semiconductor usage to the peripheral region where drive TFTs are located, away from the main display area. This spatial separation minimizes the impact of any potential optical degradation on display quality while still capturing the mobility benefits in the drive circuit region
Solution Approach 2:
The patent accepts that oxide semiconductor may have some optical degradation characteristics but uses it only in regions where optical performance is less critical (peripheral drive circuit area rather than display area). This pragmatic approach prioritizes functional performance where needed while accepting minor compromises in non-critical areas
4Device complexity
If drive circuits are integrated on the same substrate, then device complexity is reduced and downsizing is enabled, but manufacturing precision requirements increase
Solution Approach 1:
The patent uses local material differentiation (a-Si for pixels, oxide semiconductor for drives) combined with region-specific processing conditions to achieve uniform results across different functional areas. The selective etching process is optimized to work with the specific material stack in each region, maintaining manufacturing precision while enabling full integration
Solution Approach 2:
The patent adjusts processing parameters (such as etching conditions, deposition temperatures) according to the specific material composition in each region. This parameter optimization ensures that the BCE process and other manufacturing steps achieve the required precision despite the presence of multiple different semiconductor materials on the same substrate
Data Source
AI summary
A TFT substrate includes: a first semiconductor layer made of a-Si, disposed on a gate insulation layer, facing to a first gate electrode; a first and a second contact layers made of oxide having semiconductor characteristics and each partially disposed in contact with the first semiconductor layer; a first and a second electrodes connected with the first and the second contact layers, respectively; a second semiconductor layer having the same composition as the first contact layer, disposed on the gate insulation layer, facing to a second gate electrode; a third and a fourth electrodes having the same composition as the first electrode and each partially disposed in contact with the second semiconductor layer; and a pixel electrode made of oxide having conductive characteristics and the same composition as the first contact layer, disposed on an insulation layer in a first region, connected with the second electrode.