IGZO TFT Pixel Circuit Layout With Tuned Subthreshold Swing
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Solution Overview
Problem
Conventional display panels require complex film layer stacking and multiple masks due to the use of different types of thin film transistors (TFTs) for drive and switch transistors, leading to high manufacturing costs.
Innovation Solution
The display panel utilizes only IGZO-type thin film transistors with varying sub-threshold swing values, where a first-type TFT with a larger swing value serves as the drive transistor and a second-type TFT with a smaller swing value serves as the switch transistor, optimizing the film structure and reducing the number of masks needed in the manufacturing process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If different types of TFTs (LTPS for drive transistor, IGZO for switch transistor) are used in the pixel circuit, then the drive performance and switching performance are ensured, but the film layer stacking becomes complex and the number of masks increases leading to high manufacturing cost
Solution Approach 1:
The patent changes the electrical parameters of the IGZO TFT by adjusting the thickness of the active layer and gate insulating layers, and modifying the gate voltage, to achieve different sub-threshold swing values. This allows a single IGZO TFT type to exhibit both drive transistor characteristics (larger sub-threshold swing) and switch transistor characteristics (smaller sub-threshold swing), eliminating the need for multiple TFT types while maintaining required performance
Solution Approach 2:
The patent makes the IGZO TFT universal by designing it to can function as both drive transistor and switch transistor through parameter adjustment. The same basic structure and material composition can be tuned to serve different functional roles within the pixel circuit, reducing device complexity and manufacturing steps
2Reliability
If different types of TFTs are used in the pixel circuit, then the required performance is achieved, but more masks are needed for the process leading to high manufacturing cost
Solution Approach 1:
The patent achieves performance differentiation through parameter changes rather than material or structural changes. By adjusting active layer thickness, gate insulating layer thickness, and operating voltage, the same IGZO TFT structure can be optimized for either drive or switch functionality, eliminating the need for separate fabrication processes and reducing mask requirements
Solution Approach 2:
The patent employs homogeneous material composition (IGZO) for all TFTs in the pixel circuit, using the same basic structure and fabrication process. The differentiation between drive and switch transistors is achieved through parameter tuning rather than material heterogeneity, simplifying the manufacturing process and reducing costs
Data Source
AI summary
A display panel includes a substrate, and an array layer disposed on one side of the substrate. The array layer includes a first-type thin film transistor and a second-type thin film transistor. The first active layer of the first-type thin film transistor and a second active layer of the second-type thin film transistor are both metal oxide active layers, and a sub-threshold swing value of the first-type thin film transistor is greater than a sub-threshold swing value of the second-type thin film transistor.