TFT Backplate Gate Isolation Layer Thickness Variation
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Solution Overview
Problem
Existing oxide semiconductor TFT backplate structures lack differentiation in electrical properties between switch TFTs and drive TFTs, which are essential for optimal performance in flat panel displays, as they require distinct subthreshold swing values for efficient charge/discharge and current control.
Innovation Solution
A TFT backplate structure is designed with distinct configurations for switch and drive TFTs, utilizing IGZO semiconductor layers and ITO pixel electrodes, where the first gate isolation layer isolates the source/drain of the switch TFT and the first and second etching stopper layers, along with the second gate isolation layer, isolate the source/drain of the drive TFT, allowing for different electrical properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the same manufacture process is used for both switch TFT and drive TFT, then the manufacturing complexity is reduced, but the electrical properties cannot be differentiated to meet different functional requirements
Solution Approach 1:
The patent applies local quality by making the gate isolation layer thickness location-specific: the first gate isolation layer under the switch TFT has a first thickness, while the second gate isolation layer under the drive TFT has a second thickness different from the first. This local variation in thickness enables different electrical properties (subthreshold swing values) for each TFT type without requiring completely different manufacture processes, thus resolving the contradiction between adaptability and manufacturing complexity.
2Reliability
If the etching stopper layer structure is used to protect the oxide semiconductor layer, then the stability is improved, but the coupling capacitance increases which reduces manufacturing yield and increases cost
Solution Approach 1:
The patent extracts the etching stopper layer function from being universally applied and instead integrates the protective function into the gate isolation layer structure itself. The gate isolation layer with controlled thickness provides both the isolation function and sufficient protection for the oxide semiconductor layer during etching processes, eliminating the need for a separate etching stopper layer and reducing coupling capacitance while maintaining stability.
3Ease of manufacture
If the back channel etching structure or coplanar structure is used to eliminate one mask, then the manufacturing cost is reduced, but the stability of the oxide semiconductor layer deteriorates
Solution Approach 1:
The patent changes the critical parameter of gate isolation layer thickness to achieve both protection and process simplification. By optimizing the thickness parameters of the gate isolation layer, the structure provides sufficient protection for the oxide semiconductor layer during etching while allowing for simplified manufacturing processes. The specific thickness values are chosen to balance protection needs with the desire to minimize coupling capacitance and manufacturing complexity.
Data Source
AI summary
A includes a switch TFT and a drive TFT. The switch TFT is formed of a first source and a first drain, a first gate, and a first etching stopper layer, and a first oxide semiconductor layer and first gate isolation layer sandwiched therebetween. The drive TFT is formed of a second source and a second drain, a second gate, and a second oxide semiconductor layer, and a first etching stopper layer and a second gate isolation layer sandwiched therebetween. The electrical properties of the switch TFT and the drive TFT are different. The switch TFT has a smaller subthreshold swing to achieve fast charge and discharge, and the drive TFT has a relatively larger subthreshold swing for controlling a current and a grey scale more precisely.